Beware of having one or two large clients that make up most of your revenue. While that may be necessary in the beginning, you don't want to have to close your doors if you lose a major client.
These large clients also have the power to dictate terms to you, whereas smaller clients are not as demanding.
A good read by Susan Solovic on "Don't put all your eggs in one basket: 8 Strategies to diversify your small business". Some good pointers there, except the last one which speaks about their local states.
An extract from the Business Advice for Law Firms e-book by AJS